Method and system to facilitate image guided surgery

ABSTRACT

A method and system to facilitate image guided surgery by projecting onto the patient an image corresponding to markings made on pre-acquired images of the patient is disclosed. The image is projected by an imaging projecting device such as a laser which emits coherent visible light. The position of the patient and the image are determined in the same frame of reference. The markings made on the pre-acquired images are then mapped onto the corresponding locations of the patient. The image projecting device then projects images onto the patient corresponding to the markings made on the pre-acquired images. The image is projected substantially normal to a surface of the corresponding locations on the anatomical body to decrease errors arising from the image being optically distorted by the surface features of the patient. The images projected by the image projecting device can be marked onto the patient so that they are visible after the image projecting device stops emitting radiation. Use of a photodynamic substance can also be used in conjunction with the light emitted from the laser to treat tumors and other abnormalities in the patient.

RELATED APPLICATION

[0001] This application is a continuation-in-part of U.S. applicationSer. No. 09/396,472 filed Sep. 15, 1999 and entitled “Method and Systemto Facilitate Image Guided Surgery”.

FIELD OF THE INVENTION

[0002] This invention relates generally to image guided surgery. Morespecifically, the present invention relates to a method and system whichfacilitates use of pre-acquired images of an anatomical body to pre-planand perform medical procedures.

BACKGROUND OF THE INVENTION

[0003] In recent years, image guided surgery has become more and morecommon, in part because of the ability of a surgeon to view internalimages of a patient's anatomy and pre-plan a medical operation. In thisway, pre-acquired images of the anatomical body are used to plan thecourse of the medical procedure, whether the medical procedure isdiagnostic, therapeutic or surgical in nature. The pre-acquired imagescan also be used, to some extent, during the medical procedure fororientation of the surgeon with respect to the internal anatomy of thepatient.

[0004] The images of a patient's external or internal anatomy used inimage guided surgery can be generated by a number of means, includingcomputerized tomography (CT), magnetic resonance imaging (MRI), video,ultrasound and X-rays. Images may also be captured using angiography,single photon emission computer tomography and positron emissiontomography (PET). In all cases, at least two, and generally more thantwo, images of the patient's internal anatomy are generated. The imagesare captured such that the relative position of the images is known. Theimages, along with information indicating the relative position of theimages, can then be stored in a data-base to essentially create adata-base body comprised of the pre-acquired images and corresponding tothe anatomical body of the patient at the time the images were captured.

[0005] This data-base body of images can be used for a number ofpurposes, including diagnosis or to pre-plan the medical procedure. Inaddition, it is known in the art to process this data-base body ofpre-acquired images in order to produce images of various views, as wellas three-dimensional images, based on the relative spatial relationshipof the pre-acquired images within the internal anatomical structure ofthe patient.

[0006] Surgeons can pre-plan the course of a medical procedure bymarking, either manually or electronically, on the data-base body ofpre-acquired images the course of the medical procedure. The markingscan indicate areas of interest, objects of concern, as well as proposedcuts or drilling locations and orientations, and locations which must beirradiated with specific types of radiation for diagnostic ortherapeutic procedures. During the medical procedure, the surgeon canthen refer to the markings on the images to assist in performing theprocedure.

[0007] Furthermore, the prior art imaging devices can project arepresentation of the instrument or tool being used by the surgeon ontothe pre-acquired images during a medical procedure. The representationcorresponds to the position of the actual instrument or tool withrespect to the patient. By viewing the position of the representation ofthe instrument or tool with respect to the data-base body ofpre-acquired images, the surgeon can extrapolate the position of theactual probe or instrument with respect to the internal anatomy of thepatient. In addition, the surgeon can simultaneously follow thepreplanned markings on the pre-acquired images.

[0008] However, the prior art imaging devices and methods suffer fromthe disadvantage that the surgeon's attention is no longer directedsolely toward the patient during the surgery, but rather is alsodirected toward the pre-acquired images, the pre-planned markings andthe representations of the probes and instruments on the images. Inother words, during image guided surgery, the surgeon's attention issplit between the patient and the data-base image of the patient. Thisis often disconcerting for surgeons, and in particular surgeons who areunfamiliar with image guided surgery, because their attention is nolonger solely directed toward the patient, as is the case with othertypes of surgery. Rather, the surgeons must view the image of thepatient and the representation of the probes and instruments withrespect to the data-base image while manipulating the actual probes andinstruments within the patient. This can adversely affect the surgeon'shand-eye coordination and could result in the surgeon becomingdisoriented.

[0009] Also, because the attention of surgeons during image guidedsurgery is split between the patient and the image of the patient, thereis a risk that a surgeon will not notice that the surgeon has stuck, orwill strike, a “critical structure” within the patient. Criticalstructures include an organ or blood vessel, which, if struck, cancritically or severely damage the patient. This is compounded by thefact that several imaging techniques do not provide detailed images ofcritical structures, such as organs or blood vessels, and a surgeon maynot immediately see them if the surgeon's attention is directed towardsthe pre-acquired images rather than at the patient.

[0010] A further disadvantage of the prior art imaging systems is thatall pre-planned markings made by the surgeon are located on thepre-acquired images. Accordingly, in order to use the pre-plannedmarkings, the surgeon must constantly refer to the images and orient theimages and pre-planned markings to the anatomical body during the courseof the medical procedure.

SUMMARY OF THE INVENTION

[0011] Accordingly, it is an object of this invention to at leastpartially overcome the disadvantages of the prior art. Also, it is anobject of this invention to provide a method and system to facilitateimage guided surgery by projecting onto the anatomical body during themedical procedure any markings made onto the data-base body ofpre-acquired images.

[0012] Accordingly, in one of its aspects, this invention resides in asystem for projecting onto an anatomical body markings made on adata-base body of pre-acquired images of the anatomical body, saidsystem comprising: a spatial determinator for determining spatialpositional information of the anatomical body in a frame of referenceand generating first positional signals indicative of the spatialpositional information of the anatomical body in the frame of reference;a mapping unit for receiving first positional signals indicative of thespatial positional information of the anatomical body in the frame ofreference, mapping the markings made on the data-base body ofpre-acquired images onto corresponding locations on the anatomical bodyand generating a mapping signal indicative of the correspondinglocations in the frame of reference of the markings on the data-basebody; and an image projecting device for receiving the mapping signaland projecting an image of the markings made on the data-base body ontothe corresponding locations of the anatomical body.

[0013] In a still further aspect, the present invention provides asystem for projecting onto an anatomical body markings made on adata-base body of pre-acquired images of the anatomical body, saidsystem comprising: a spatial determinator for determining spatialpositional information of the anatomical body by tracking the anatomicalbody in a frame of reference and generating first positional signalsindicative of the spatial positional information of the anatomical bodyin the frame of reference; a mapping unit for receiving first positionalsignals indicative of the spatial positional information of theanatomical body in the frame of reference, mapping the markings made onthe data-base body of pre-acquired images onto corresponding locationson the anatomical body and generating a mapping signal indicative of thecorresponding locations in the frame of reference of the markings on thedata-base body; and an image projecting device for receiving the mappingsignal and projecting an image of the markings made on the data-basebody onto the corresponding locations of the anatomical body, said imageprojecting device projecting the image substantially normal to a surfaceof a portion of the corresponding locations of the anatomical body.

[0014] In a further aspect, the present invention resides in a methodfor projecting onto an anatomical body markings made on a data-base bodyof pre-acquired images of the anatomical body, said method comprisingthe steps of: obtaining spatial positional information of the anatomicalbody in a frame of reference; mapping the markings made on the data-basebody of pre-acquired images onto the corresponding locations on theanatomical body; and projecting an image of the markings made on thedata-base body onto the corresponding locations of the anatomical bodyin the frame of reference.

[0015] In a further aspect, the present invention provides a method forprojecting onto an anatomical body markings made on a data-base body ofpre-acquired images of the anatomical body, said method comprising thesteps of: obtaining spatial positional information of the anatomicalbody by tracking the anatomical body in a frame of reference; mappingthe markings made on the data-base body of pre-acquired images ontocorresponding locations on the anatomical body; and projecting an imageof the markings made on the data-base body onto the correspondinglocations on the anatomical body in the frame of reference substantiallynormal to a surface of a portion of the corresponding locations of theanatomical body.

[0016] One of the advantages of the present invention is that an imagecorresponding to the markings made by the surgeon onto the data-basebody of pre-acquired images can be viewed during the surgical proceduredirectly on the patient. In other words, the surgeon will have thebenefit of any markings made on the pre-acquired images duringpre-planning of the medical procedure while the surgeon's attention isdirected to the patient. This permits the surgeon to more easily performthe medical procedure in a manner that the surgeon is accustomed to,rather than by watching the pre-acquired images and a representation ofthe instruments on the images.

[0017] A further advantage of the present invention is that theattention of the surgeon will be directed towards the patient forgreater periods of time during the medical procedure. This will assistin the surgeon identifying critical structures, which may or may nothave appeared in the pre-acquired images, before they are struck. Also,even if the critical structures have appeared on the pre-acquiredimages, the internal anatomy of the patient may have changed since thepre-acquired images were captured. For example, the internal organs orveins of a patient could have moved, either by movement of the patient,the actual incision by the surgeon, or other means. Clearly, thesemovements will not be reflected in the pre-acquired images as themovements occurred after the pre-acquired images were captured and thesurgeon will only notice the changes by viewing the patient.

[0018] Another advantage of the present invention is that a surgicalprocedure can be planned by a surgeon located remote from the patient,and, with only the benefit of the pre-acquired images. For instance, themarkings made on the pre-acquired images by the surgeon at the remotelocation will be projected onto the patient to assist the surgeonlocated proximate to the patient in performing the medical procedure. Inaddition, both surgeons can continue to mark the pre-acquired images inorder to mutually identify the organs in the patient and thecorresponding images of the organs in the pre-acquired images. In thisway, telesurgery can be facilitated. Furthermore, in a preferredembodiment, the remote surgeon could initially mark portions of theanatomical body with a beam which is only visible to the remote surgeonand not visible to the local surgeon. For instance, the remote surgeoncould mark the pre-acquired images to identify organs in the patientwith an infrared laser. The infrared laser may be visible to a remotesurgeon if the camera used by the remote surgeon can see infrared beams.However, the infrared beam would not be visible to the local surgeon.This may be advantageous by allowing the remote surgeon to take a momentand carefully draw and/or edit a region of interest entirely “inprivate” before projecting an image to the local surgeon using visiblelight which the local surgeon can see. In this way, the local surgeon isnot distracted while the remote surgeon becomes satisfied with themarkings which one surgeon desires to show to the local surgeon. Thistechnique can also be used for teaching purposes, or any other purposein which the remote surgeon desires to mark specific areas which canonly be seen by one surgeon and not the other surgeons.

[0019] Another advantage of the present invention is that the imagesprojected by the image projecting device can be marked, eithertemporarily or permanently, onto the patient. This can be performed byhaving an image projecting device which emits radiation that canpermanently mark a patient, such as by use of a CO₂ laser which couldmark the image onto the anatomy of the patient, either on the skin or onthe bone. In a similar manner, use of an ultraviolet laser could be usedto leave a mark on the skin of the patient corresponding to markingsmade to the pre-acquired images. Likewise, use of a photoreactive inkwhich perceptively changes in response to radiation emitted by the imageprojecting device can be used to temporarily mark the patient withmarkings made to the pre-acquired images. In a preferred embodiment, thephotoreactive ink may be either thermochromic ink, which reacts toinfrared radiation, or, photochromic ink which can react to differenttypes of radiation, such as ultraviolet radiation. More preferably, thephotoreactive ink may be embedded in a material, such as plastic, whichis draped over the patient and then marked with the radiation emitted bythe image projecting device, rather than applying the substance to thesurface of the patient. In this way, the photoreactive ink embedded inthe marking material would perceptively change and the image appear onthe marking material, rather than the image appearing on a substanceapplied to the patient. In either case, a surgeon can quickly andaccurately mark onto the patient any markings made onto the imagesduring preplanning, such that the markings will appear on the anatomicalbody after the image projecting device ceases projecting the image.

[0020] In another aspect of the present invention, the markings on thepre-acquired images can correspond to areas or tumors which must beirradiated as part of a photodynamic therapeutic procedure. In otherwords, substances which can change cells of the patient, such asphotodynamic agents which react to specific types of radiation to becomecytotoxic, can be applied to the patient. The image projecting devicecan be programmed to emit the types of radiation to which thephotodynamic agent reacts. In this way, portions of the patient, such astumors, can be eliminated or destroyed in a precise and predeterminedmanner by irradiating the patient with the specific type of radiation ina pre-planned manner. Also, because the radiation will be applied in aspecific and pre-planned manner, a higher level of accuracy can beobtained for irradiating the patient, and therefore a more generalphotodynamic agent can be used which may be partially absorbed by thehealthy tissue, as only the tumors will be irradiated. Likewise, a moreintense beam of light can be used because it is less likely that healthytissues will be irradiated.

[0021] Another advantage of the present invention is that the imageprojecting device can emit radiation to cauterize an area of the body.In this way, the area of the patient which is to be cauterized, such asthe portion of the brain around a tumor that is to be removed, can bepre-planned and executed automatically once the tumor has been removed.

[0022] In a further embodiment, the image is projected substantiallynormal to a surface of the corresponding locations or a portion of thecorresponding locations. In this way, by projecting the imagesubstantially normal to a surface of the corresponding locations of theanatomical body, a clearer image is produced and optical distortions arereduced. Preferably, the image projecting device projects the imagewithin 45 degrees of the normal of the surface where the correspondinglocations are located. More preferably, the image projecting deviceprojects the image within 30 degrees of the normal of the surface wherethe corresponding locations are located. If the corresponding locationsextend over a large surface of the patient such that it is not possibleto have a single image projecting device which can project an imagesubstantially normal to the surface having the corresponding locations,the image projecting device may comprise more than one emitter such thatdifferent portions of the image will be projected by different emitters,each emitter projecting its portion of the image substantially normal toa part of the surface where the corresponding locations are located. Inthe event where two emitters are not practical, or, an entire image canstill not be projected substantially normal to the entire surface wherethe corresponding locations are located, the portion of the image whichis not substantially normal to a surface can be projected in a differentmanner, such as with dashed lines or in a different color, to bring tothe attention of the surgeon that part of the image may contain opticaldistortion errors due in part to the image not being projected normal tothe surface of the patient, or by surface features of the patient.

[0023] In a further embodiment, the image projecting device is thenmoved to a location which optimally projects the image onto theanatomical body. This position is generally determined to be a positionwhereby the projected beam is incident substantially normal to thesurface upon which the image is being projected. Preferably, theincident angle is within 45 degrees, and more preferably 30 degrees, ofthe normal of the surface. To facilitate this, preferably the positionand orientation of the image projecting device is tracked in the frameof reference. In this way, optical distortion errors have been found tobe decreased, thereby improving their overall image projected by theimage projecting device.

[0024] Further aspects of the invention will become apparent uponreading the following detailed description and drawings which illustratethe invention and preferred embodiments of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

[0025] In the drawings, which illustrate embodiments of the invention:

[0026]FIG. 1 shows a symbolic representation of a system according toone embodiment of the present invention;

[0027]FIG. 2 is a further symbolic representation of a system accordingto one embodiment of the present invention to project an image;

[0028]FIG. 3 is a symbolic representation of a system according to oneembodiment of the present invention used to guide a drill;

[0029]FIG. 4 is a symbolic representation of a system according to oneembodiment of the present invention used to diagnose or treat a patient;

[0030]FIG. 5 is a symbolic representation of a system according to afurther embodiment of the present invention which tracks the position ofthe image projecting device;

[0031]FIG. 6A illustrates the projection of an image onto the anatomicalbody from an image projecting device at two different positions;

[0032]FIGS. 6B and 6C illustrate the projected image from the twodifferent positions shown in FIG. 6A;

[0033]FIG. 7 is a symbolic representation of a system according to afurther embodiment of the present invention with a swivel and tilt baseunit; and

[0034]FIG. 8 is a symbolic representation of a further embodiment of thepresent invention where the spatial determinator moves with the imageprojecting device.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0035]FIG. 1 illustrates the system, shown generally by referencenumeral 10, according to one embodiment of the present invention. Asshown in FIG. 1, the system 10 comprises a spatial determinator 5 whichcan determine spatial positional information for various objects in theframe of reference 2. The frame of reference 2, which is shownsymbolically by the xyz origin, is generally the frame of reference 2within which the patient 6 is located.

[0036] The spatial determinator 5 can be any type of device which candetermine the spatial position of objects in the frame of reference 2.However, in a preferred embodiment, the spatial determinator 5 comprisesan optical tracking system which utilizes two cameras 8 and 9 to trackthe position and orientation of objects in the frame of reference 2 andsend position signals P_(S) indicative of the spatial positionalinformation of the objects being tracked in the frame of reference 2. Itis understood that the spatial positional information may includeinformation regarding the position, as well as the orientation, of theobject in the frame of reference 2.

[0037] One object which the spatial determinator 5 tracks in the frameof reference 2 is an anatomical body which, in the embodiment shown inFIG. 1, corresponds to the patient 6. The spatial determinator 5 willdetermine the spatial position of the patient 6 and generate firstpositional signals P_(S1) indicative of the spatial positionalinformation of the anatomical body 6 in the frame of reference 2.

[0038] The first positional signals P_(S1) are received by a mappingunit 12M which, in the embodiment shown in the FIG. 1, is contained in acomputer 12. It is understood that the mapping unit 12M can be containedwithin any physical structure which can execute the functions of themapping unit 12M and the computer 12 shown in FIG. 1 is simply presentedas a representation of one possible physical structure within which themapping unit 12M may be contained.

[0039] The mapping unit 12M is connected to a storage unit 14 withinwhich pre-acquired images 11 of the anatomical body 6 are stored. Thepre-acquired images 11 stored within the storage unit 14 can form adata-base body 13 of the patient 6, as is known in the art. The storageunit 14 can comprise any type of storage medium to store the data-basebody 13 of pre-acquired images 11 for use by the mapping unit 12M.

[0040] In addition to the data-base body 13 of pre-acquired images 11,the storage unit 14 will also have stored thereon any markings, showngenerally by reference numeral 18M, made on the data-base body 13. Inother words, if a surgeon or other person has made markings 18M on thedata-base body 13, these markings will be stored in the storage unit 14and can be accessed by the mapping unit 12M. The markings 18M may bestored either with the images 11 or separately with an indication of howthe markings 18M relate to the data-base body 13 of pre-acquired images11.

[0041] The mapping unit 12M receives the first positional signal P_(S1)from the spatial determinator 5 indicating the spatial positionalinformation of the anatomical body 6 in the frame of reference 2. Themapping unit 12M then maps the markings 18M made on the data-base body13 of pre-acquired images 11 onto corresponding locations of theanatomical body 6. In order to accomplish this, a registrationprocedure, as is known in the art, will generally be performed toregister key features on the anatomical body 6 to corresponding keyfeatures on the data-base body 13.

[0042] In a further preferred embodiment, a compensation procedure canbe performed. The compensation procedure follows the initialregistration procedure. In the compensation procedure, a control pointis selected in the frame of reference 2. Preferably, the control pointis on or near the anatomical body 6. The image projecting device 16 thenprojects an image onto the control point. The position that isilluminated is then determined using the spatial determinator 5. Thedifference between the control point and the point illuminated by thelaser is then determined. This difference is recorded as an error thatis used to correct any systematic errors, such as numerical round-offerrors, which may be present in the system. This difference can then beused as a compensation value which can be included in the system tocompensate for the numerical or systematic errors.

[0043] The mapping unit 12M will then generate a mapping signal M_(S)indicative of the corresponding locations in the frame of reference 2 ofthe markings 18M made on the data-base body 13. In other words, themapping signal M_(S) will comprise the xyz positional information of thecorresponding locations in the frame of reference 2, and likely on theanatomical body 6, of the markings 18M made on the data-base body 13. Incases where the orientation of the markings 18M is relevant, the mappingsignal M_(S) will also comprise the information regarding theorientation of the markings 18M in the frame of reference 2. The mappingsignal M_(S) is then received by an image projecting device 16. Theimage projecting device 16 can comprise a laser or other imageprojecting device 16 which can project an image onto any position in theframe of reference 2.

[0044] The image projecting device 16 projects an image, shown generallyby reference numeral 18I, based on the mapping signal M_(S). The image18I corresponds to the markings 18M made on the data-base body 13, butprojected onto the corresponding locations of the anatomical body 6 inthe frame of reference 2. For example, if a surgeon had marked thepre-acquired images 11 with a marking 18M indicating the incision to bemade, the image 18I will correspond to the location on the anatomicalbody 6 where the marking 18M for the incision was made on the data-basebody 13.

[0045] In a preferred embodiment, the image projecting device 16projects the image 18I in a manner which can be tracked by the spatialdeterminator 5. In this way, the spatial determinator 5 can track theimage 18I and determine the spatial information for the image 18I in theframe of reference 2. The spatial determinator 5 can then generate asecond positional signal P_(S2) indicative of the spatial positionalinformation of the image 18I in the frame of reference 2. The mappingunit 12M receives the second positional signal P_(S2) in addition to thefirst positional signal P_(S1) and can determine whether or not theimage 18I being projected by the image projecting device 16 correspondsto the position of the markings 18M made on the data-base body 13 ofpre-acquired images 11. If the mapping unit 12M detects a disparitybetween the actual location of the image 18I being projected and theintended location of the projection, the mapping unit 12M can send amodified mapping signal M_(S) to correct the disparity and project amore accurate image 18I.

[0046] Preferably, the image projecting device 16 can project the imageby emitting radiation which is perceptible by the spatial determinator5. For example, if the spatial determinator 5 comprises an opticaltracking system having cameras 8 and 9, the cameras 8 and 9 can sense orperceive the radiation being emitted by the image projecting device 16,and thereby generate the second positional signal P_(S2) indicative ofthe spatial positional information of the image 18I in the frame ofreference 2. If the cameras 8 and 9 of the optical tracking systemcannot track visible radiation, it will be necessary for the imageprojecting device 16 to first project the image 18 by emitting radiationwhich is perceptible to the cameras 8, 9. Once the mapping unit 12M hasdetermined that the image 18I being projected corresponds to themarkings 18M made on the data-base body, the projecting device 16 willthen emit radiation which is visually perceptible. In a furtherembodiment, the projecting device 16 will emit radiation which marks theimage 18I onto the anatomical body 6 such that the markings appear onthe anatomical body after the image projecting device ceases projectingthe image.

[0047] In a further preferred embodiment, to ensure that the image 18Iappears correctly at the corresponding location, it is preferred thatthe image projecting device 16 projects the image 18I substantiallynormal to a surface 28S of a portion of the corresponding locations ofthe anatomical body 6. In this way, optical distortion errors can bedecreased. Furthermore, for images 18I projected after an incision hasbeen made, it is less likely that another object, such as a part of theanatomical body 6, interferes with the projection of the image 18I.Preferably, the image 18I is projected within 45 degrees, and morepreferably within 30 degrees, of the normal of the surface 28S having aportion of the corresponding locations.

[0048] In order to project the image 18I substantially normal to thesurface 28S of the portion of the corresponding locations, it isgenerally necessary to orient the image projecting device 16 withrespect to the anatomical body 6 such that the image 18I can beprojected substantially normal to the surface 28S. This can beaccomplished by either moving the anatomical body 6 or moving the imageprojecting device 16.

[0049] In a preferred embodiment, the system 10 comprises translationdevice 16T shown symbolically in FIG. 1. The translation device 16Treceives translation signals T_(S), generally from the mapping unit 12M,or another unit designed to generate the translation signals T_(S), tomove the image projecting device 16 to a position and orientation suchthat the image projecting device 16 projects the image 18I substantiallynormal to the surface 28S of the portion of the corresponding locations.In order to accomplish this, it is also generally necessary for themapping unit 12M to know the position of the image projecting device 16in the frame of reference 2. In one embodiment, this can be accomplishedby the translation device 16T monitoring how the image projecting device16 is moved, such as by using stepper motors or an encoder.Alternatively, the spatial determinator 5 can track the movement of theimage projecting device 16 in the frame of reference 2 and generateimage projecting position signals P_(S1) indicative of the position ofthe image projecting device 16 in the frame of reference 2. The mappingunit 12M then receives the image projecting position signals P_(S1) andsends the translation signal T_(S) to the translation device 16T to movethe image projecting device 16 to a position and orientation withrespect to the anatomical body 6 such that the image projecting device16 can project the image 18I substantially normal to the surface 28S ofthe portion of the corresponding locations.

[0050] In a preferred embodiment, the normal to the surface 28S arecalculated by the mapping unit 12M from the pre-acquired images 11stored in the storage unit 14, as is known in the art. Preferably, inorder to confirm the calculated normals, the image projecting device 16projects known images, such as triangles, onto the surface 28S prior tothe procedure commencing. The known images projected on the surface 28Sof the anatomical body 6 can then be monitored to determine if theprojected known images appear in a manner consistent with the calculatednormals. For instance, when an optical tracking system utilizing cameras8 and 9 is used for the spatial determinator 5, the cameras 8, 9 canmonitor the known images projected on the anatomical body 6. The knownimages can then be analyzed to determine planes, and normals to theseplanes. For instance, if triangles are used, the vertices of thetriangles are used to form planes from which normals can be calculated.These normals represent the actual normals of the surfaces on theanatomical body 6 and these actual normals are compared to thecalculated normals from the database body 13 to ensure they areconsistent. If they are not consistent, revised calculations are madeand/or now images may be required.

[0051] Preferably, the computer 12 also comprises an input unit 12I forinputting information, including instructions and data. For example, theinputting unit 12I can be used to input additional markings 18M onto thedata-base body 13. In this way, a surgeon can continuously make markings18M on the database body 13 during the procedure. The projecting device16 can then project images 18I of the markings 18M, including themarkings made through the input unit 12I, onto the patient 6.

[0052] In addition, if several markings 18M are made on the data-basebody 13 of pre-acquired images 11, the input unit 12I can be used toinput information comprising instructions as to which marking 18M theimage projecting device 16 should be projecting. For example, during asurgical procedure, the surgeon may have marked onto the data-base body13 markings 18M reflecting the incision, the position and orientation ofan entry point, as well as internal features of the patient 6 whichshould be treated. Accordingly, the input unit 12I can be used by thesurgeon to input instructions as to which markings 18M should beprojected during different stages of the surgical procedure. Inaddition, if the projecting device 16 can project two different images18I simultaneously, such as if the projecting device 16 emits a firstcoherent beam of visible light and a second coherent beam of visiblelight, the surgeon can use the input unit 12I to select not only whichmarkings 18M are being projected, but also which coherent beam of lightis being used to project the corresponding images 18I. This isparticularly useful if the image projecting device 16 emits a secondcoherent beam of visible light which is of a different wavelength, andtherefore different colour, than the first coherent beam of visiblelight, so that the surgeon can easily distinguish between the two images18I being projected.

[0053] It is also understood that the input unit 12I need not be locatedproximate the computer 12. In other words, a surgeon located remote fromthe second frame of reference 2 can have an input unit 12I and sendinformation, including instructions as to additional markings 18M and aselection of the markings 18M to be projected to the computer 12. Inthis way, telesurgery can be facilitated by the surgeon locatedproximate the patient 6 immediately seeing the projection of the image18I, the markings 18M being made and selected by a remotely locatedsurgeon. This facilitates image guided surgery by permitting a remotelylocated surgeon to guide the proximately located surgeon through theprocedure by projecting images 18I of the marking 18M made by theremotely located surgeon directly onto the patient 6.

[0054] Likewise, if two surgeons are located proximate the patient 6,both surgeons can also use the input unit 12I to non-obtrusivelyidentify portions of the patient's 6 anatomy by marking the portion onthe data-base body 13 and then having the image projecting device 16project the image 18I corresponding to the markings 18M. This could alsobe used by instructors to identify items of interest in a non-evasivemanner by projecting the image 18I onto the items of interest, ratherthan touching the actual items of interest.

[0055] It is understood that the input unit 12I can comprise any type ofmeans for inputting information. For example, the input unit 12I cancomprise a keyboard or a mouse. The input unit 12I can also bevoice-activated such that a surgeon can send verbal commands to theinput unit 12I as to which markings 18M should be projected.

[0056]FIG. 2 shows a further embodiment of the present invention. InFIG. 2, the image projecting device 16 comprises a laser which emits acoherent beam of visible light, such as laser beam 22. It is understoodthat the image projecting device 16 may be calibrated or otherwiseregistered so that it could direct the laser beam 22 to a known positionin the frame of reference 2 in response to the mapping signals M_(S). Inorder to assist in directing the laser beam 22, the system 10 cancomprise translation devices 16T which can move the image projectingdevice 16 such that the laser beam 22 will have the proper position and,if desired, orientation. In a further embodiment, as discussed above,the translation devices 16T move the image projecting device 16 inresponse to the translation signals T_(S) to a position and orientationsuch that the image projecting device 16 projects the image 18Isubstantially normal to a surface 28S of the portion of thecorresponding locations.

[0057] In a preferred embodiment, the spatial determinator 5 tracks theposition of the image projecting device 16. This may assist incalibrating or registering the image projecting device 16 in the frameof reference 2. Also, if the image projecting device 16 comprisestranslation devices 16T, the spatial determinator 5 can track theposition of the image projecting device 16 and send the image projectingsignal P_(SI) to the mapping unit 12M indicative of the position of theimage projecting device 16 in the frame of reference 2. The mapping unit12M can then determine whether or not the image projecting device 16 hasbeen moved by the translation devices 16T to the correct position toproject image 18I of the markings 18M made on the data-base body 13 ontothe corresponding locations of the anatomical body 6 in the frame ofreference 2 and substantially normal to a surface 28S of the portion ofthe corresponding locations.

[0058] As also illustrated in FIG. 2, it is preferred that the spatialdeterminator 5 be located proximate the image projecting device 16 inthe frame of reference 2. In this way, it will be possible for thespatial determinator 5 to easily track the image 18I being produced bythe laser beam 22. Also, it is desirable to have the spatialdeterminator 5 and the image projecting device 16 proximate to eachother and out of the way from the surgeons and other medical equipment.In this regard, it is preferable that both the spatial determinator 5and the image projecting device 16 be located in otherwise unused space,such as near the ceiling of the operating room.

[0059] In a preferred embodiment, as illustrated in FIG. 8, the spatialdeterminator 5 is associated with the image projecting device 16 suchthat the image projecting device 16 and the spatial determinator 5 willmove together. In this way, the position of the image projecting device16 need not be explicitly determined by the spatial determinator 5.Rather, the position of the image projecting device 16 in the frame ofreference 2 will be the same as the position of the spatial determinator5 such that the image projecting position signals P_(SI) correspond tothe position of the spatial determinator 5 in the frame of reference 2.This is advantageous for several reasons. For instance, to any extentthat the image projecting device 16 and spatial determinator 5 movetogether, their frames of reference will be related. This will increasethe accuracy of the overall system by decreasing the transformationsbetween the image projecting device 16 frame of reference and thespatial determinator 5 frame of reference. Furthermore, the volumewithin which the spatial determinator 5 can track objects is oftenlimited. Therefore, by not tracking the image projecting device 16,which is generally located near the spatial determinator 5, the spatialdeterminator 5 can track a larger volume around the operating site,including the anatomical body 6 and the images 18I being projected ontothe anatomical body 6.

[0060]FIG. 8 shows an improved translation device 16T which comprises aswivel/tilt base unit 160 having a pan rotary table 162 and a tiltrotary table 164, which components are described in more detail belowwith respect to FIG. 7. For present purposes, however, it should beunderstood that the spatial determinator 5 need not be fixed to theswivel/tilt base unit 160, but rather could be only fixed or associatedwith the translation portion of the translation device 16T. In thisembodiment, not shown in FIG. 8, the spatial determinator 5 would bemoved within the image projecting device 16 in the frame of reference 2,but would not be rotated by the swivel/tilt base unit 160 with the imageprojecting device 16. This is particularly advantageous where thespatial determinator 5 is bulky or heavy and cannot be easily moved bythe swivel/tilt base unit 160, but can be moved by the translationportion of the translation device 16T.

[0061] The patient 6, also referred to as the anatomical body, in FIG. 2is positioned on a table, such as an operating table 20. As shown inFIG. 2, the image projecting device 16 will project the image 18I ontothe patient 6.

[0062] If the image 18I comprises a circle or other two-dimensionalrepresentation, the image projecting device 16 can quickly move thelaser beam 22 to produce the image 18I. The laser beam 22 can be movedrapidly by the image projecting device 16 so that the viewer willperceive a substantially continuous image 18, represented by the dottedline on the patient 6 in FIG. 2, by the persistence of vision effect.The image projecting device 16 will generally comprise a pair of mirrorswhich can move quickly to produce the image 18I. If desired,fluorescence or other methods could also be used. It is understood thatas the surface upon which the image 18I will be projected will be thesurface of an anatomical feature of the patient 6, and therefore notnecessarily flat. The projecting device 16 and the mapping unit 12M willcompensate for the shape of the anatomical feature of the patient 6 sothat image 18I of the markings 18M made on the data-base body 13 appearon the corresponding locations of the anatomical body of the patient 6even though the surface is not flat, and, projecting the image 18Isubstantially normal to a surface 28S containing the correspondinglocations of the anatomical body 6. If it is not possible to project theimage 18I substantially normal to the entire surface 28S, the imageprojecting device 16 will attempt to project the image 18I normal to thesurface 28S of at least a portion of the corresponding locations.

[0063] It is understood that the image 18I can be any type of twodimensional representation. For instance, in one embodiment as describedabove, the image projecting device 16 could be produced by one or morecoherent beams which can move over the surface 28S to create the image18I. In this case, preferably, the angle of incidence of the one or morecoherent beams are substantially normal to the surface 28S of at least aportion of the corresponding locations as the beam is scanned over thesurface 28S to produce the image 18I. This is described in more detailbelow with respect to FIGS. 6A, 6B and 6C. The image 18I could also be afixed image generated from a slide or computer generation techniques. Inthis case, the image 18I would be preferably projected such that theimage 18I is substantially normal to the surface of at least a portionof the corresponding locations.

[0064] In addition, the laser beam 22 could be configured such that itcan mark the image 18I onto the patient 6. This can be accomplished, forexample, by using an image projecting device 16 which emits a laser beam22 that can mark the patient 6 with the image 18I such that the image18I will appear even after the laser beam 22 is no longer emittingradiation. For example, use of a projecting device 16 which comprises aCO₂ or ultraviolet laser could mark the image 18I onto the anatomy, suchas either on the skin or on the bone, of the patient 6. In this way,once the image 18I has been temporarily or permanently marked on thepatient 6, the image projecting device 16 can then cease projecting theimage 18I and discontinue emitting the laser beam 22.

[0065] In a preferred embodiment, use of photoreactive ink, showngenerally by reference numeral 28 in FIG. 2, can be applied to thepatient 6. The photoreactive ink 28 would preferably react to theradiation emitted by the image projecting device 16, such as the laserbeam 22, and change in a visually perceptible manner in response to thelaser beam 22. The image projecting device 16 can be designed to emitradiation of different wavelengths so that one wavelength can bevisually perceived and the other wavelength can cause the substance toperceptively change. In this way, the image 18I projected by the imageprojecting device 16 would be temporarily or permanently marked onto thepatient 6 by means of the photoreactive ink perceptively changing inresponse to the emitted radiation. Accordingly, in this way, themarkings 18M made on the data-base body 13 can be easily transferred totemporary or permanent markings on the patient 6 by means of theprojected image 18I. In this case, it is understood that radiationemitted by the image projecting device 16 need not be visuallyperceptible, but only cause the photoreactive ink 28 to react in aperceptible manner. Alternatively, in a further preferred embodiment,the photoreactive ink 28 is not placed directly on the patient 6, butrather is embedded in a marking material, shown generally by referencenumeral 28M in FIG. 2. The marking material 28M can be applied to theanatomical body 6 such that projecting the image 18I in a type ofradiation to which the substance 28 reacts onto the marking material 28Mwill mark the marking material on the anatomical body 6 with the image18I projected by the image projecting device 16. In this way, the image18I can be marked indirectly on the patient 6 by marking the image 18Ion the marking material 28M.

[0066] It is understood that any type of photoreactive substance 28 canbe used either directly on the patient 6, or, embedded in the markingmaterial 28M. Preferably, the photoreactive ink 28 will react to a typeof radiation which is not present ordinarily in the operating room,either in terms of wavelength, intensity or characteristics. Forexample, the photoreactive ink 28 could react to infrared radiation orultraviolet radiation, which are not generally present in the operatingroom in intensities sufficient to cause the photoreactive ink 28 tootherwise react in a perceptible manner. Radiation of various otherwavelengths could also be used. In other applications, x-ray radiationor even particle beams, could be used to cause the substance 28 to reactin a perceptible manner.

[0067]FIG. 2 also shows a tracking tool 24 attached to the patient 6 bymeans of a support 25. The tracking tool 24 can assist in tracking theposition and orientation of the patient 6 in the frame of reference 2.In a preferred embodiment, where the spatial determinator 5 comprises anoptical tracking system having cameras 8 and 9, the tracking tool 24will have tracking emitters or reflectors 26 which can be perceived bythe cameras 8, 9. In this way, the cameras 8, 9 can easily track theposition of the tracking elements 26 and thereby determine the positionand orientation of the patient 6 in the frame of reference 2. Thetracking tool 24 can comprise any type of tracking tool, such as thetracking tool described in U.S. Pat. No. 5,834,759 which is incorporatedherein by reference.

[0068] In a further preferred embodiment as illustrated in FIG. 5, atracking tool 54, similar to the tracking tool 24, is attached to theimage projecting device. The tracking tool 54 is attached to the imageprojecting device 16 by support 55. The tracking tool 54 has trackingelements 26 which, in a preferred embodiment, can be easily tracked bythe cameras 8, 9. This facilitates tracking the position and orientationof the image projecting device 16 in the frame of reference by thespatial determinator 5. The spatial determinator 5 can then send theimage projecting signal P_(SI) to the mapping unit 12M. In this way, themapping unit 12M can determine the position of the image projectingdevice 16, and, whether or not the image projecting device 16 has beenmoved by the translation device 16T to the correct position. In analternate embodiment, the translation device 16T comprises a steppermotor or encoder which accurately monitors its movement and the movementof the image projecting device 16. The position of the image projectingdevice 16 in the frame of reference 2 can then be determined by signalsP_(SI) from the step promoter or encoder. In either case, the mappingunit 12M will receive position signals P_(SI) indicative of the positionof the imaging projecting device 16 in the frame of reference 2.

[0069]FIG. 3 shows a further embodiment of the present invention. InFIG. 3, the image projecting device 16 is projecting the laser beam 22at an entry point 18E into the patient 6.

[0070] It is apparent from a comparison of FIGS. 2 and 3 that the entrypoint 18E corresponds to a specific point on the image 18I shown in FIG.2. In other words, in FIG. 2 the image projecting device 16 isprojecting the image 18I of a first marking 18M made on the data-basebody 13 which represents the portion of the skull of the patient 6 whichis to be removed. In FIG. 3, the image projecting device 16 isprojecting the image of the entry point 18E which corresponds to themarkings 18M made on the data-base body 13 indicating the desired entrypoint to the patient 6 in order to remove the portion of the skullrepresented by image 18I. The projecting device 16 could either projectthe image 18I or the image of the entry point 18E according to thesignals inputted from the input unit 12I as discussed above.Alternatively, both the image 18I and the image of the entry point 18Ecould be projected at the same time.

[0071] In the case of the entry point 18E, a surgeon may be concernednot only with the position of the entry point 18E, but also theorientation of the entry point 18E. The markings 18M on the data-basebody 13 would likely include a vector having a position, as well as anorientation, to uniquely identify the entry point in six degrees offreedom. Accordingly, the image of the entry point 18E will have anorientation and position which corresponds to both the position andorientation of the markings 18M made on the database body 13.

[0072] As shown in FIG. 3, the orientation and position of the laserbeam 22, which corresponds to the markings 18M made on the data-basebody 13, can be used by the surgeon to align instruments, such as drill30, for entry into the patient 6. It is apparent that as the surgeonaligns the drill 30 by means of the laser beam 22, the surgeon will havethe benefit of seeing the image of the entry point 18E corresponding tothe markings 18M made on the data-base body 13, as well as be able toobserve the drill 30 as it cuts into the entry point 18E of the patient6. In this way, the surgeon will not only know that the position of thedrill 30 corresponds to the markings 18M made on the data-base body 13,but the surgeon will also be able to view the drill 30 entering into theentry point 18E. This will assist the surgeon in orienting the drill 30,as well as permit the surgeon to become immediately aware of any“critical structures” which may be encountered by the drill 30, even ifthese “critical structures” did not appear on the pre-acquired images11.

[0073] The drill 30 may also be attached to a tracking tool 34, similarto the tracking tool 24 attached to the patient 6. The tracking tool 34can comprise tracking elements 36 which are tracked by the cameras 8, 9when the spatial determinator 5 comprises an optical tracking system. Inthis way, the drill 30 can also be tracked in the frame of reference 2and a representation of the tool 30 may appear on the data-base body 13of pre-acquired image 11. As such, the surgeon will have the benefit ofboth viewing the orientation and position of the markings 18M projectedby the image projecting device 16 on the patient 6, as well as viewing arepresentation of the drill 30 on the data-base body 13 of pre-acquiredimages 11, as is done on conventional systems.

[0074] In a further preferred embodiment, the system 10 may generate anaudible alarm if the position of the drill 30, as perceived by thecameras 8, 9 deviates from the orientation and position of the markings18M as represented by the laser beam 22. In this way, the surgeon willbe immediately advised if the drill 30 does not follow the path of themarkings 18M made on the data-base body 13 of pre-acquired images 11.

[0075]FIG. 4 shows a further embodiment of the present invention. InFIG. 4, a portion of the skull of the patient 6 has been removed. Itwill be apparent from a comparison of FIGS. 2 and 4 that the hole in theskull 40 corresponds to the image 18I made by the image projectingdevice 16 and illustrated in FIG. 2. Accordingly, the surgeon hasremoved a portion of the skull 40 as pre-planned and as projected by theimage 18I onto the patient 6 as shown in FIG. 2.

[0076] With the portion of the skull removed, a treatment area 42 isrevealed. In a preferred embodiment, the image projecting device 16 canalso be used to diagnose and/or treat the patient 6 as follows.

[0077] As shown in FIG. 4, a radiation detecting device 48 is present todetect radiation from the anatomical body 6. The radiation detectingdevice 48 has a field of view 46 and will detect radiation reflectedfrom the anatomical body 6, and more specifically the treatment area 42of the anatomical body 6. In this way, the image projecting device 16can project diagnostic images 18D, and if desired, with different typesof radiation, into the treatment area 42 corresponding to markings 18Mmade on the data-base body 13. The radiation from the diagnostic image18D will be reflected towards the field of view 46 of the radiationdetecting device 48. By using different types of radiation, theradiation detecting device 48 will be able to analyze the radiationdetected from the treatment area 42 of the anatomical body 6 todetermine characteristics of the anatomical body 6 being radiated by theimage projecting device 16. In this way, diagnostic procedures can beperformed within the treatment area 42 based on diagnostic markings 18Dpreviously made to the data-base body 13.

[0078] It is understood that the image detecting device 48 comprises adetector 49 which detects the radiation reflected from the anatomicalbody 6 in field of view 46. The radiation detecting device 48 alsocomprises the electronics to analyze the radiation detected from theanatomical body 6 to determine the characteristic of the anatomical bodybeing irradiated. Rather than having the electronics located proximatethe detector 49, the electronics can be located in another location, andcould be contained within the computer 12. Also, while the detector 49for the radiation detecting device 48 is shown separate from the spatialdeterminator 5, in one embodiment where the spatial determinator 5comprises an optical tracking system, the cameras 8, 9 of the opticaltracking system may also be used as the detector 49 for the radiationdetecting device 48 if the cameras 8, 9 can detect the type of radiationbeing reflected from the anatomical body 6.

[0079] Also, as shown in FIG. 4, in addition to the image projectingdevice 16, a second separate beam source 44 which emits beam 45 could beused in addition to, or in replacement of, the image projecting device16 and the beam 22. Of course, if the beam source 44 is to project animage 18D corresponding to the markings 18M made on the data-base body13, it will be necessary for the beam source 44 to receive signalscorresponding to the mapping signals M_(S), as is done by the imageprojecting device 16.

[0080] In a further preferred embodiment, the system 10 can be used totreat the patient 6. This can be done in one manner by applying asubstance to the anatomical body 6 which reacts to a specific type ofradiation. Preferably, the reaction would cause cells of the anatomicalbody 6 to which the substance and radiation have been applied to change.For example, the substance can become cytotoxic and kill the cells inits vicinity in reaction to specific types of radiation. For example,the substance may comprise a photodynamic agent which is applied eitherto the surface of the treatment area 42, intravenously or orally by thepatient 6. The photodynamic agent can be taken up non-preferentially bythe healthy tissue, as well as any tumours, in the patient 6. Thephotodynamic agent can then react to the radiation from the laser beam22 to change the cells of the anatomical body 6 such as by becomingcytotoxic and killing the cells in the vicinity.

[0081] Because the images 18D can be projected in a precise manner toirradiate objects in the treatment area 42, corresponding to markings18M on the data-base body 13, more precise irradiation of the treatmentarea 42 can be accomplished. In this way, only the tumours within thetreatment area 42 can be irradiated, thereby providing more precisephotodynamic therapy. Also, because of the precision of the applicationof the radiation by means of the projecting device 16, more generalphotodynamic agents can be used which may be partially absorbed by thehealthy tissue, as well as the tumour, because the laser beam 22 willonly be directed to an image corresponding to the markings 18M on thetumour in the data-base body 13. For the same reasons, a more intenselaser beam 22 could be used.

[0082] In a similar manner, an intense laser beam 22 can be used withouta substance, such as a photodynamic agent, to treat the patient 6. Forexample, if a tumour bed has been marked on the data-base body 13, anintense beam, such as from a CO₂ laser, can be used to cauterize thetumour bed. In this way, the tumour bed, or other portion of theanatomical body 6, can be cauterized in a rapid and precise manner.

[0083] It is understood that the image detecting device 48 comprises adetector 49 that detects the radiation reflected or emitted by means ofa photonic interaction from the anatomical body 6 or a debris plume 47.The second beam source 44, and if desired, a third beam source (notshown) could be used to induce a photonic reaction in the plume 47,including non-linear optical effects, Raman or fluorescent scattering orsimilar effects to determine partial or complete composition of theplume 47 or components thereof. Using the well-known principle of“differential absorption”, it is possible to determine the chemicalcomposition of the plume 47 by comparing the relative absorption of twoclosely tuned laser beams 22, 45.

[0084] In addition, the system 10 can be used in other procedures inorder to treat the patient 6. For example, tattoos or other surfaceblemishes may appear on pre-acquired images 11. The tattoos can bemarked by markings 18M on the data-base body 13 formed by thepre-acquired images 11. The image projecting device 16 can then emitradiation which will blanch the tattoos or other surface blemishes in arapid and precise manner corresponding to markings 18 made on thedatabase body 13.

[0085] As described above, in order to improve the precision andaccuracy of the image 18I, and decrease optical distortions, it ispreferred that the image projecting device 16 project the image 18Isubstantially normal to a surface 28S where at least a portion 28P ofthe corresponding locations 28C are located on the anatomical body 6.This is illustrated in FIG. 6A which shows the image 18I projected attwo different points, namely Point A and Point B. FIG. 6A shows thenormals NA and NB to the surface 28S at two points, namely Point A andPoint B. When the image projecting device 16 is at position 1, there arelarge angles A1, B1 with respect to the normals NA, NB at points A andB. These angles A1, B1 are generally larger than about 30 degrees withthe normal NA, NB. Because of this, the image projected at Point A willhave optical distortion errors, as illustrated by the oval identified byreference numeral 180E in FIG. 6B. However, if the image projectingdevice 16 is at position 2, the image 18I would be substantially normalto the surface 28S of the portion 28P of the corresponding locations 28Cof the anatomical body 6 and there would be smaller angles A₂, B₂ withrespect to the normals NA, NB at Points A, B. Because of this, the image18I projected at Point A, as well as Point B, would be much moreprecise, as illustrated by the dot identified by reference numeral 180Pin FIG. 6C.

[0086] If the image 18I is produced by rapidly scanning a coherent beamof light over the portion 28P of the corresponding locations, then it isclear that having the smaller angles A₂, B₂ with respect to the normalsNA, NB will produce a more accurate and clearer image 18I. Furthermore,if the image 18I is produced by projecting a fixed image, such as aslide or computer generated image, then preferably the angle ofincidence of the image 18I is substantially normal to the surface 28S ofat least a portion of the corresponding locations.

[0087] Accordingly, FIGS. 6A, 6B and 6C illustrate that projecting theimage 18I substantially normal to the surface 28S of a portion 28P ofthe corresponding locations 28C of the anatomical body 6 decrease theoptical distortion errors and improves precision and accuracy of theimage 18I. To accomplish this, the image projecting device 16 ispreferably oriented with respect to the anatomical body 6 such that theimage 18I projected by the image projecting device 16 forms an anglewithin about 45 degrees, and more preferably about 30 degrees, with thenormal NA, NB of the surface 28S of the portion 28P of the correspondinglocations 28C.

[0088] As described above, in order to orient the image projectingdevice 16, the system 10 preferably comprises a translation device 16T.The translation device 16T can move the image projecting device 16within the frame of reference 2. Furthermore, the image projectingdevice 16 and the translating device 16T comprise mirrors (not shown)which can change the position and orientation of the image beingprojected by the image projecting device 16. In the embodiment where theimage projecting device 16 comprises an emitter of coherent light, suchas a laser, the image projecting device 16 may also comprise mirrors(not shown) having a range of either 20 degrees or 40 degrees, forexample, to change the orientation and/or position of the emittedcoherent beam of light.

[0089] However, in some cases, the orientation and/or position of theemitted beam of light from the image projecting device 16 must bealtered more than this amount. Accordingly, in a preferred embodiment,the translation device 16T comprises a swivel/tilt base unit 160, asshown in FIG. 7. The swivel/tilt base unit 160 comprises a pan rotarytable 162 and a tilt rotary table 164 which permit the image projectiondevice 16 to be oriented over a larger range of positions andorientations. As illustrated in FIG. 7, a tracking device 54 is attachedto the image projecting device 16 in order to track its position andorientation in the frame of reference 2.

[0090] In the event that the corresponding location 28C is too large sothat the image 18I can be projected substantially normal to the entiresurface 28S, it is preferred that the image 18I be separated into twoportions, namely the first portion 18I₁ and the second portion 18I₂. Thefirst portion 18I₁ will be known to be projected substantially normal tothe surface 28S of the portion 28P of the corresponding locations 28C.The second portion 18I₂ will be known not to be substantially normal tothe surface 28S of the portion 28P of the corresponding locations 28C.In order to indicate this to the surgeon, thereby advising the surgeonof the potential errors inherent in the second image 18I₂, the secondimage 18I₂ is projected in a manner perceptively different from themanner in which the first image 18I₁ is projected, as shown in FIG. 7.For instance, the first image 18I₁ may be projected in solid lines andthe second image 18I₂ may be projected in dashed lines. Alternatively,different wavelengths, and therefore colours, could be used for thefirst image 18I₁ and the second image 18I₂.

[0091] In order to have more of the image 18I substantiallyperpendicular to the surface 28S of the portion 28P of the correspondinglocation 28C, the image projecting device 16 may have more than oneemitter. For example, as shown in FIG. 5, the system 10 may have animage projecting device 16 with a second emitter 16S which can be movedby the translation device 16T to a position and orientation to projectan image 18I, such as by emitting visible light, substantially normal toa surface 28S of another portion of the corresponding locations 28C. Ifthe two emitters emit light having the same wavelength, the fact thatthere are two separate emitters may not even be apparent to the surgeon.For any portion of the image 18I which still cannot be projected normalto a surface 28S, two perceptively different manners of projecting thenon-normal image can be used, as described above.

[0092] It understood that while the present invention has been describedin terms of the anatomical body 6 of the human, the system 10 and methodof using the system 10 are not limited to use on humans. Rather, thesystem 10 and method of using the system 10 can be used in veterinaryand other applications where an image of markings made on pre-acquiredimages 11 must be projected onto the corresponding locations of theobjects from which the images were acquired.

[0093] It is also understood that while the present invention has beendescribed and illustrated in terms of a surgical procedure on the skullof the patient 6, the invention is not limited to this application.Rather, the invention can be used in any type of surgical procedurewhere projection of images corresponding to the markings 18M made onpre-acquired images 11 will facilitate image guided surgery.

[0094] It is understood that while the present invention has beendescribed and illustrated in terms of certain types of translationdevices 16T for moving the image projecting device 16 to a position andorientation such that the image projecting device 16 projects the image18 substantially normal to the surface 28S of a portion 28P of thecorresponding locations, the invention is not limited to these specifictypes of translation devices 16T. Rather, the present invention includesall types of devices which can perform the function of moving the imageprojecting device 16 to a position and orientation such that the imageprojecting device 16 projects the image 18 substantially normal to thesurface 28S of a portion 28P of the corresponding locations. Withoutlimiting the foregoing, this would include robots or robot arms whichcan move the image projecting device 16 in the frame of reference 2.

[0095] It is also understood that while the invention has been describedin some embodiments as comprising a coherent beam of light, thisinvention is not limited to coherent beams of light, but rather couldcomprise other beams of light, such as collimated beams of light.

[0096] It will be understood that, although various features of theinvention have been described with respect to one or another of theembodiments of the invention, the various features and embodiments ofthe invention may be combined or used in conjunction with other featuresand embodiments of the invention as described and illustrated herein.

[0097] Although this disclosure has described and illustrated certainpreferred embodiments of the invention, it is to be understood that theinvention is not restricted to these particular embodiments. Rather, theinvention includes all embodiments which are functional, electrical ormechanical equivalents of the specific embodiments and features thathave been described and illustrated herein.

The embodiments of the invention in which an exclusive property orprivilege is claimed are defined as follows:
 1. A system for projectingonto an anatomical body markings made on a data-base body ofpre-acquired images of the anatomical body, said system comprising: aspatial determinator for determining spatial positional information ofthe anatomical body by tracking the anatomical body in a frame ofreference and generating first positional signals indicative of thespatial positional information of the anatomical body in the frame ofreference; a mapping unit for receiving first positional signalsindicative of the spatial positional information of the anatomical bodyin the frame of reference, mapping the markings made on the data-basebody of pre-acquired images onto corresponding locations on theanatomical body and generating a mapping signal indicative of thecorresponding locations in the frame of reference of the markings on thedata-base body; and an image projecting device for receiving the mappingsignal and projecting an image of the markings made on the data-basebody onto the corresponding locations of the anatomical body, said imageprojecting device projecting the image substantially normal to a surfaceof a portion of the corresponding locations of the anatomical body. 2.The system as defined in claim 1 wherein the image projecting deviceprojects the image substantially normal to the surface of the portion ofthe corresponding locations by projecting the image at an angle withinabout 30 degrees of the normal of the surface of the portion of thecorresponding locations.
 3. The system as defined in claim 1 wherein theimage projecting device emits a coherent beam of light; and wherein theimage projecting device is oriented with respect to the anatomical bodysuch that the coherent beam of light is within about 30 degrees of thenormal of the surface of the portion of the corresponding locations. 4.The system as defined in claim 3 wherein the normal of the surface ofthe corresponding locations of the anatomical body are calculated fromthe pre-acquired images.
 5. The system as defined in claim 4 wherein thenormal of the surface of the corresponding locations of the anatomicalbody calculated from the pre-acquired images are confirmed by the imageprojecting device projecting known images on the portion of the surfaceof the anatomical body and monitoring the known images to determine ifthe projected known images appear in a manner consistent with thecalculated normals.
 6. The system as defined in claim 1 furthercomprising translation devices for moving the image projecting device inresponse to a translation signal to a position and orientation such thatthe image projecting device projects the image substantially normal tothe surface of the portion of the corresponding locations.
 7. The systemas defined in claim 6 wherein the spatial determinator tracks theposition and orientation of the image projecting device in the frame ofreference and generates image projecting position signals indicative ofthe position of the image projecting device in the frame of reference;and wherein the mapping unit receives the image projecting positionsignals, and sends the translation signal to the translation device tomove the image projecting device to a position and orientation withrespect to the anatomical body such that the image projecting deviceprojects the image substantially normal to the surface of the portion ofthe corresponding locations.
 8. The system as defined in claim 1 whereinthe image projecting device emits a coherent beam of light which canmark the anatomical body such that the image of the markings projectedby the image projecting device will appear on the anatomical body afterthe image projecting device ceases projecting the image.
 9. The systemas defined in claim 1 further comprising: a substance which reacts to atype of radiation by changing in a perceptible manner; wherein the imageprojecting device emits the type of radiation to which the substancereacts; and wherein the substance can be applied to the anatomical bodysuch that projecting the image in the type of radiation to which thesubstance reacts onto the anatomical body will mark the anatomical bodywith the image projected by the image projecting device.
 10. The systemas defined in claim 1 further comprising: a marking material havingembedded therein a substance which reacts to a type of radiation bychanging in a perceptible manner; wherein the image projecting deviceemits the type of radiation to which the substance reacts; and whereinthe marking material can be applied to the anatomical body such thatprojecting the image in the type of radiation to which the substancereacts onto the marking material will mark the marking material on theanatomical body with the image projected by the image projecting device.11. The system as defined in claim 10 wherein the type of radiation isselected from the group consisting of infrared radiation, ultravioletradiation, x-ray radiation and particle beams.
 12. The system as definedin claim 1 further comprising: a substance which reacts to a specifictype of radiation by changing cells of the anatomical body to which thesubstance has been applied; and wherein projecting the image in the typeof radiation to which the substance reacts onto the anatomical bodychanges the cells of a portion of the anatomical body to which thesubstance is applied and the type of radiation is projected.
 13. Thesystem as defined in claim 7 wherein the spatial determinator comprisesan optical tracking system to track objects in the frame of reference;and wherein the optical tracking system optically tracks the anatomicalbody in the frame of reference and generates the first positionalsignals indicative of the spatial positional information of theanatomical body in the frame of reference.
 14. The system as defined inclaim 13 wherein the image projected by the image projecting device canbe tracked by the optical tracking system; and wherein the opticaltracking system tracks the image projected by the image projectingdevice and generates second positional signals indicative of the spatialpositional information of the image in the frame of reference; andwherein the mapping unit receives the first positional signals andsecond positional signals and determines whether the image beingprojected by the image projecting device corresponds to the markingsmade on the data-base body of pre-acquired images.
 15. The system asdefined in claim 14 wherein if the mapping unit determines that theimage being projected by the image projecting device does not correspondto the markings made on the data-base body, the mapping unit regeneratesthe mapping signal to cause the projecting device to project a moreaccurate image of the markings made on the data-base body.
 16. Thesystem as defined in claim 13 wherein the optical tracking system isproximate the image projecting device in the frame of reference.
 17. Thesystem as defined in claim 16 wherein the translation devices move theoptical tracking system with the image projecting device, such that theimage projecting position signals correspond to a position of theoptical tracking system in the frame of reference.
 18. The system asdefined in claim 16 further comprising a first optical tracker fixed tothe anatomical body and a second optical tracker fixed to the imageprojecting device; and wherein the optical tracking system tracks theanatomical body in the frame of reference by tracking the first andsecond optical trackers.
 19. The system as defined in claim 1 furthercomprising: radiation detecting device for detecting radiation from theanatomical body; wherein the image projecting device projects the imageof the markings made on the data-base body onto the correspondinglocations of the anatomical body using types of radiation which can bereflected from the anatomical body towards the radiation detectingdevice; and wherein the radiation detecting device analyzes theradiation detected from the anatomical body to determine acharacteristic of the anatomical body being irradiated by the imageprojecting device.
 20. The system as defined in claim 19 wherein thespatial determinator comprises an optical tracking system to trackobjects in the frame of reference; wherein the optical tracking systemoptically tracks the anatomical body in the frame of reference andgenerates the first positional signals indicative of the spatialpositional information of the anatomical body in the frame of reference;and wherein the optical tracking system and the radiation detectingdevice share a common radiation detector.
 21. The system as defined inclaim 1 further comprising: a storage unit for storing said data-basebody of pre-acquired images, said storage unit being connected to themapping unit; an input unit connected to said storage unit for inputtinginformation, said information comprising markings made onto thedata-base body of pre-acquired images; wherein information correspondingto markings made on the data-base body of pre-acquired images can beinputted at all times; and wherein the image projected by the imageprojecting device can comprise the markings made on the data-base bodyby information inputted through the input unit.
 22. The system asdefined in claim 3 wherein a first portion of the image is projectedsubstantially normal to the surface of the portion of the correspondinglocations and a second portion of the image is projected other thansubstantially normal to the surface of the portion of the anatomicalbody; and wherein the first portion of the image is projected in a firstmanner and the second portion of the image is projected in a secondmanner perceptively different from the first manner.
 23. The system asdefined in claim 22 wherein the image projecting device emits a firstcoherent beam of visible light having a first wavelength and a secondbeam of coherent light having a second wavelength perceptively differentfrom the first wavelength; and wherein the first portion of the image isprojected in the first wavelength and the second portion of the image isprojected in the second wavelength.
 24. The system as defined in claim 6wherein the image projecting device comprises a first coherent beam oflight emitter for emitting visible light having a first wavelength and asecond coherent light emitter for emitting visible light having a secondwavelength wherein the translation devices can move the first emitterwith respect to the second emitter.
 25. The system as defined in claim24 wherein the translation devices move the first emitter to a positionand orientation to emit visible light substantially normal to thesurface of the portion of the corresponding location and the secondtranslation devices move the second emitter to a position andorientation to emit visible light substantially normal to a surface ofanother portion of the corresponding locations.
 26. The system asdefined in claim 3 wherein the image projecting device emits a firstcoherent beam of visible light having a first wavelength and a secondcoherent beam of visible light having a second wavelength different fromthe first wavelength; and wherein the information inputted into theinput unit selects which markings made on the data-base body areprojected by the first coherent beam of visible light and the secondcoherent beam of visible light.
 27. A method for projecting onto ananatomical body markings made on a data-base body of pre-acquired imagesof the anatomical body, said method comprising the steps of: obtainingspatial positional information of the anatomical body by tracking theanatomical body in a frame of reference; mapping the markings made onthe data-base body of pre-acquired images onto corresponding locationson the anatomical body; and projecting an image of the markings made onthe data-base body onto the corresponding locations on the anatomicalbody in the frame of reference substantially normal to a surface of aportion of the corresponding locations of the anatomical body.
 28. Themethod as defined in claim 27 further comprising the steps of projectingthe image with an image projecting device; and marking the anatomicalbody with the image projected by the image projecting device such thatthe image projected by the image projecting device will appear on theanatomical body after the image projecting device ceases projecting theimage.
 29. The method as defined in claim 27 wherein the imageprojecting device projects the image at an angle within about 30 degreesof the normal of the surface of the portion of the correspondinglocations.
 30. The method as defined in claim 27 further comprising thesteps of: projecting the image with an image projecting device whichemits a coherent beam of light; and orienting the image projectingdevice with respect to the anatomical body such that the coherent beamof light is within about 30 degrees of the normal of the surface of theportion of the corresponding locations.
 31. The method as defined inclaim 30 further comprising the preliminary steps of: (a) calculatingthe normal of the surface of the corresponding locations from thepre-acquired images; and (b) confirming the calculated normals of thesurface of the corresponding locations by (i) projecting known images onthe surface of the corresponding locations; and (ii) monitoring theknown images to determine if the projected known images appear in amanner consistent with the calculated normals.
 32. The method as definedin claim 27 further comprising the steps of: projecting the image withan image projecting device; determining the position and orientation ofthe image projecting device in the frame of reference; and moving theimage projecting device to a position and orientation such that theimage projecting device projects the image substantially normal to thesurface of the position of the corresponding locations.
 33. The methodas defined in claim 27 further comprising the step of: temporarilymarking the anatomical body with the image projected by an imageprojecting device.
 34. The method as defined in claim 33 furthercomprising the steps of: applying a substance to the anatomical bodywhich reacts to a specific type of radiation by changing in aperceptible manner; and projecting the type of radiation to which thesubstance reacts onto the anatomical body corresponding to the markingsmade to the data-base body of pre-acquired images so that the anatomicalbody is temporarily marked with the image projected by the imageprojecting device.
 35. The method as defined in claim 27 furthercomprising the steps of: applying a substance to the anatomical bodywhich reacts to a specific type of radiation by changing cells of theanatomical body to which the substance has been applied; and whereinprojecting the image in the type of radiation to which the substancereacts onto the anatomical body changes the cells of a portion of theanatomical body to which the substance is applied and the type ofradiation is projected.
 36. The method as defined in claim 27 whereinthe step of projecting an image of the markings onto the anatomical bodycomprises the step of projecting a visible image of the markings ontothe anatomical body.
 37. The method as defined in claim 27 furthercomprising an image projecting device which emits a first coherent beamof visible light; and wherein the step of projecting an image of themarkings onto the anatomical body comprises the step of projecting avisible beam of light having a position and orientation corresponding tothe markings made on the data-base body.
 38. The method as defined inclaim 37 wherein the image projecting device emits a second coherentbeam of visible light at a different wavelength from the first coherentbeam of visible light; and wherein the first and second coherent beamsof visible light project images of different markings onto theanatomical body corresponding to the markings made on the data-base bodyof pre-acquired images.
 39. The method as defined in claim 29 furthercomprising the steps of: projecting a first portion of the image in afirst manner and projecting a second portion of the image in a secondmanner perceptively different from the first manner; and wherein thefirst portion of the image is projected within about 30 degrees of thenormal of the surface of the corresponding locations and the secondportion of the image is not within about 30 degrees of the normal of thesurface of the corresponding locations.